Electric heating apparatus



April 1940- H. F. BARIFFI 2,

ELECTRIC HEATING APPARATUS I Filed Dec. 9,1938

Invent or- Herbert F. Bar'iffi by MMZ His Attorneg.

Patented Apr. 2, 1940 UNITED STATES PATENT OFFICE ELECTRIC HEATING APPARATUS poration Application December 9, 1938, Serial No. 244,793

4 Claims.

The present invention relates to electric heating apparatus of the type having an electric heating element for heating a forced draft of air circulated by a motor driven fan.

In such systems the air circulated over or past the heating element keeps the heating element at a safe operating temperature. If the flow of air were stopped, the temperature of the heating element would rise to a dangerous degree, and might even cause the heating element to burn out.

The object of my invention is to provide an improved construction for preventing energizing of the heating element when the fan is not operating.

For a consideration of what I believe novel and my invention, attention is directed to the following description and the claims appended thereto.

The single figure of the accompanying drawing is a diagrammatic view of heating apparatus embodying my invention.

R ferring to the drawing, there is shown an electric heating element I having associated therewith a fan 2 for circulating a forced draft of air over the heating element which heats the air. The fan is mounted on a shaft 3 suitably driven (in a manner not shown) by an electric motor 4 which is illustrated as a single phase motor having a starting winding 5 and a running winding 6. The running winding is at all times connected to the motor terminals 1 and 8 which in turn are connected by conductors 9 and Hi to line conductors II and I2. A switch I3 is connected in the line conductor II. The starting winding 5 has one end connected to the motor terminal I and the other end connected through a conductor I4, a switch I5, and a conductor l6 to the motor terminal 8. The switch has contacts I1 and I8 which are normally closed and which are opened when the motor reaches a predetermined speed so as to open the starting winding circuit. Switches of this type are well known in the art. For purposes of illustration I have shown the switch as operated by a centrifugal device I9 mounted on a shaft driven by the motor. The centrifugal device comprises a collar 2| fixed to the shaft and a collar 22 slidable on the shaft and connected to the switch I5, Links 22 are respectively pivoted on the collars 2| and 22 and are connected to weights 24.

Upon rotation of the shaft 20, the weights 24 fly Y outward, lowering the sliding collar 22 and opening the switch contacts I1 and I0. This construction is illustrative of constructions well known in the art for shifting from starting to running connections when the motor reaches a predetermined speed. The particular switch operating construction is not important in my invention. The coil of a normally open relay 25 is connected across the switch contacts I! and I8. When the switch contacts are closed, the relay coil is short circuited and the relay contacts 26 and 21 are accordingly open. The relay contact 21 is connected to the heating element I in turn connected to the line conductor II. The relay contact 26 is connected to the other side of the line I2. When the contacts 26 and 21 are open, the heating element is accordingly deenergized. The heating element is energized by closure of the contacts 26 and 21 by a bridging member 28 carried by the-relay 25.

To start the operation, the switch I3 is closed. Since the motor is at rest, the contacts I1 and I8 are closed and the motor is in its starting condition. Upon reaching a predetermined speed, the switch I5 is operated by the centrifugal device III to open the contacts I! and I8. This opens the circuit to the starting winding and shifts the motor connections to the running condition. Opening of the contacts I1 and I8 connects the relay coil 25 in series with the starting winding 5 and energizes the relay, causing the bridging member 28 to close the contacts 26 and 21 and thereby energize the heating element I. Since at this time the motor is running at the required speed, the fan 2 is circulating a stream of air over the heating element. This prevents overheating of the heating element. Upon reduction of the motor speed, the switch contacts I1 and it are closed by the centrifugal device I9, short circuiting the relay and permitting its bridging member 28 to open the circuit through contacts 28 and 21. With the above-described arrangement it is impossible to energize the heating element unless the motor is running.

What I claim as new and'desire to secure by Letters Patent of the United States is:

1. In combination, an electric heating unit, a fan for circulating air over the unit, a driving motor for the fan having starting and running windings, a switch'ior opening the starting winding circuit at a predetermined motor speed, a relay connected across the contacts of said switch whereby it will be energized when the switch is open, and contacts operated by said relay for energizing said heating unit.

2. In combination, an electric heating unit, a fan for circulating air over the unit, a driving motor for the fan having starting and running windings, a. relay for energizing said heating unit, and a switch for connecting the relay in series with the starting winding at a predetermined motor speed.

3. In combination, an electric heating unit, a.

fan for circulating air over the unit, a driving motor for the fan having starting and running connections, and means including a switch for shifting from the starting to the running connection and for energizing said heating unit at a predetermined motor speed.

HERBERT F. BARIFFI. 10 

